Plant Gene and Trait 2024, Vol.15, No.1, 44-51 http://genbreedpublisher.com/index.php/pgt 45 poplar a more viable feedstock for bioenergy (Biswal et al., 2015; Pawar et al., 2017; Li et al., 2021). Moreover, understanding the genetic regulation of these pathways can aid in the development of poplar varieties with tailored wood qualities for specific industrial needs (Ratke et al., 2018; Hassane et al., 2022). This review aims to offer insights into the genetic and biochemical pathways that can be targeted to improve wood quality in poplar, thereby advancing its utility in biofuel production and other industrial uses. 2 Glycosyltransferases Involved in Xylan Biosynthesis 2.1GT47C 2.1.1 Role in xylan backbone synthesis The GT47 family, particularly the GT47C subfamily, plays a crucial role in the synthesis of the xylan backbone. Xylan, a major hemicellulose component in plant cell walls, is synthesized by a complex of glycosyltransferases, including members of the GT47 family. These enzymes are responsible for adding xylose residues to the growing xylan chain, forming the β-1,4-linked xylose backbone essential for xylan structure and function (Anders et al., 2023). 2.1.2 Gene expression and regulation in poplar In poplar, the expression of GT47 genes is tightly regulated during wood formation. Studies have shown that the downregulation of GT47 genes in hybrid aspen leads to significant changes in xylan content and cell wall properties. For instance, the suppression of GT47 genes resulted in reduced xylan content and altered cellulose orientation, which in turn affected the overall growth and wood quality of the plants (Ratke et al., 2018). This indicates that GT47 genes are crucial for maintaining proper xylan biosynthesis and cell wall integrity in poplar. 2.2GT43 2.2.1 Contribution to xylan chain elongation The GT43 family, including the IRX9 and IRX14 clades, is essential for the elongation of the xylan chain. These enzymes work in concert to add xylose units to the xylan backbone, facilitating the formation of long xylan chains necessary for robust cell wall structure. The GT43 family has been shown to be involved in both primary and secondary cell wall xylan biosynthesis, with distinct sets of GT43 members contributing to each process (Ratke et al., 2015; Anders et al., 2023). 2.2.2 Genetic regulation and associated pathways In poplar, the expression of GT43 genes is regulated by key transcription factors involved in secondary cell wall formation. For example, the GT43B gene is activated by the transcription factors PtxtMYB021 and PNAC085, which are master regulators of secondary wall biosynthesis. This regulation ensures that GT43 enzymes are expressed in the appropriate tissues and developmental stages to facilitate proper xylan biosynthesis (Ratke et al., 2015). Additionally, the downregulation of GT43 genes in poplar has been shown to stimulate growth and reprogram the transcriptome, indicating a complex regulatory network that balances xylan biosynthesis with overall plant development (Ratke et al., 2018). 2.3GT8 2.3.1 Function in xylan branching and modification The GT8 family, particularly the GAUT12/IRX8 subfamily, is involved in the branching and modification of xylan. These enzymes add side chains and other modifications to the xylan backbone, which are crucial for the functional properties of xylan in the cell wall. In poplar, the downregulation of GAUT12 genes leads to reduced xylan and pectin content, highlighting their role in xylan modification and overall cell wall architecture (Biswal et al., 2015). 2.3.2 Regulatory mechanisms in poplar The regulation of GT8 genes in poplar involves multiple layers of control, including transcriptional and post-transcriptional mechanisms. For instance, the downregulation of GAUT12.1 in poplar results in significant changes in cell wall composition and increased growth, suggesting that GT8 genes are tightly regulated to balance
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